(a) Field of the Invention
The present invention relates to a time division duplexing radio system. More specifically, the present invention relates to an apparatus and method for separating transmitted and received signals.
(b) Description of the Related Art
Time division duplexing TDD is a technique used to transmit and receive on a single frequency by dividing one frame into a frame for transmitting and a frame for receiving. While different frequencies are used for transmitting and receiving in a conventional radio communication, the same frequency is divided into different time slots for transmitting and for receiving in time division duplexing, and therefore bidirectional communication is performed.
The time division duplexing radio system has various configurations for separating transmitted and received signals, and a configuration using a high output switch is widely used among the configurations. FIG. 1 shows a radio system using the high output switch.
As shown in FIG. 1, the conventional radio system separates a transmit signal received from a power amplifier 101 and a receive signal received from a bidirectional combiner 103 by using the high output switch 102.
The high output switch is formed by using a semiconductor as a diode, and the semiconductor causes reduction of reliability of the radio system because the performance of the semiconductor is reduced when the semiconductor is used for a long time.
An additional control signal for operating the high output switch is also required, and it is a problem that a transmit/receive control signal is externally applied to the configuration of the radio system.
A radio system using a circulator is provided as another method for effectively separating the transmit/receive signals, which is shown in FIG. 2.
As shown in FIG. 2, the conventional radio system separates the transmit and receive signals by using a single circulator 202.
Isolation between transmitters and receivers in the configuration of the radio system depends on an isolation of the circulator 202, and therefore a signal sensitivity of the receiver in the configuration is reduced because the isolation of the conventional circulator is about 20 dB. Accordingly, an additional device for protecting the receiver is required.
The published U.S. patent application Ser. No. 6,567,648 B1 is disclosed related to a method for protecting the receiver. In the method, the receiver is protected by filtering the transmit signals between signals received from an antenna and leaked transmit signals and eliminating the signals.
However, a filter and an amplifier for eliminating the leaked signals are required in the method for protecting the receiver, and therefore an additional device is still required to protect the receiver.